1. Field of the Invention
The present invention relates to a radio communication system and a radio communication terminal for performing a radio communication between radio communication terminals having system codes.
2. Description of the Related Art
A radio communication system has recently been known to the public, which includes a radio communication terminal carried by a user, such as a portable telephone, a PHS (personal handy-phone system) terminal, a pager, and a PDA (personal digital assistant), for intercommunicating sound and data with another terminal including a commonly-used domestic telephone, and a base station connected to a communication network and communicating with the radio communication terminal to connect the terminal to the network.
In this system, the radio communication terminal is driven by a secondary battery or the like such that it can be carried by a user. The radio communication terminal is capable of storing various types of data items such as callee's telephone numbers and addresses, schedule, and memorandum using characters and sound, and is also capable of transmitting/receiving information (sound, sound data, text data, image data, etc.) to/from another terminal through a telephone network.
As one example of the radio communication system, there is a PHS which is currently put to practical use in Japan. The PHS will now be described for understanding of the radio communication system.
A radio communication terminal of the PHS is employed as a slave of a master (base station) placed in a home. When the terminal is operated outdoors, it is also connected to a communication network through base stations (public and self-supporting stations) connected to the telephone network, with the result that it is allowed to intercommunicate with another terminal. If, furthermore, radio communication terminals are registered as slaves of their common master, peer-to-peer radio communication can be performed between the terminals but not through the base stations.
In the peer-to-peer communication between the radio communication terminals, since the terminals necessitate a system code of their common master, all the terminals have to be brought to the master side for previous registration setting up the relation between the master and slave. In this registration, the slave ID numbers for discriminating the terminals are registered in the master, while a system calling code (part of CS-ID) for discriminating the master is registered in the slaves. In peer-to-peer radio communication between terminals, the system calling code and slave ID numbers are transmitted between the terminals, and it is determined based on the system calling code whether the peer-to-peer radio communication is possible or not. In other words, the peer-to-peer communication cannot be performed unless the system calling codes of the slaves are identical with that of the master.
The above-described radio communication terminals have the following problem. In order to perform the peer-to-peer radio communication between the terminals, all the terminals have to be brought close to their common master and registered so as to correspond to the master. Therefore, the peer-to-peer radio communication cannot be done between a terminal and another terminal which is not registered in the master of the former one or between terminals which are registered in different masters.